Polybutene is generally prepared by polymerizing an olefin component having a carbon number of 4 (C4) derived during the naphtha degrading process using a Friedel-Craft type catalyst and has a number average molecular weight of about 300 to 5,000. Among the C4 raw materials, remainder after 1,3-butadiene extraction is called C4 raffinate-1 and includes paraffin such as isobutane, normalbutane and olefin such as 1-butene, 2-butene, and isobutene. Among these, the isobutene content is about 30 to 50 wt %. The C4 raffinate-1 is mostly used for preparation of polybutene or methyl-t-butyl ether (MTBE) which is an octane number enhancer. Since isobutene, among the olefin components of C4 raffinate-1, has the highest reactivity, the produced polybutene is mostly composed of the isobutene unit. Further, polybutene may be prepared from high purity isobutene or butane-butene oil (B-B oil), i.e. a C4 mixture derived during the crude oil refining process.
As the molecular weight increases, the viscosity of polybutene increases. Polybutene has a viscosity of about 4 to 40,000 cSt (centi-stocks) at 100° C. In addition, polybutene is pyrolyzed at a temperature of 300° C. or above without residues. Further, polybutene has a branched chain alkyl structure, thereby having good solubility to lubricating oil or fuel. Therefore, the polybutene is added to engine oil and used as an anti-scuff agent or a viscosity index improver, or mixed with fuel for an internal combustion engine of automobiles and used as a clarificant.
Typically, polybutene is mostly used for a gluing agent, an adhesive, and insulating oil so that products having high reactivity are not preferred. However, recently, a polar group is introduced to polybutene to thereby be used as a fuel clarificant or lubricating oil additive, and thus need for polybutene having high reactivity is gradually increased. Among products which is obtainable by introducing a polar group, the mostly well known and the most often used product is polyisobutenyl succinic anhydride (PIBSA) which is prepared by reacting polybutene with maleic anhydride. Most of fuel clarificants or lubricating oil additives are prepared by using the PIBSA as an intermediate. Additionally, products obtained by introducing a polar group include phenols and alkyl phenols such as polybutenylphenol prepared through manich reaction of mid-reactive polybutene (Mid-Range Vinylidene Content Polyisobutylene (MVPB)) which has 40 to 70% of vinylidene content.
When the double bond of polybutene used for PIBSA preparation is located at the terminal of polybutene, PIBSA is obtained at high yield. However, when the double bound is located at the internal of polybutene, and in particular, the number of substituted alkyl group at the double bound is high, PIBSA yield is decreased due to low reactivity caused by steric hindrance. Producing double bond at the terminal of the molecule and terminating polymerization indicate production of a compound opposite to general chemical reaction theory. The most effective way to prepare highly reactive polybutene (HRPB) having a vinylidene content of more than 70%, which is difficult to produce, is to use a complex catalyst in which a catalyst and cocatalyst are mixed.
For preparation of highly reactive polybutene and mid-reactive polybutene, boron trifluoride, as a main catalyst, and alcohol, as a cocatalyst are typically used. For mid-reactive polybutene, when polymerization is performed by using mix C4 including isobutene as a raw material and methanol or ethanol as a cocatalyst, mid-reactive polybutene is prepared with remarkably decreased efficiency. When polymerization is performed by increasing the isobutene conversion rate, there is a problem in which a large amount of light polymer (LP) in addition to the main product, i.e. mid-reactive polybutene, is generated.
Before highly reactive polybutene is used, PIBSA is prepared with normal polybutene, i.e. non-reactive polybutene (conventional polyisobutylene, ConPB, which has a vinylidene content of less than 40%). One method to increase reactivity of non-reactive polybutene is that polybutene is chlorinated through chlorination reaction using chlorine gas, and then reacted to maleic anhydride to prepare PIBSA so that the final product is achieved. However, this process requires high cost for preventing corrosion of a reactor, and a large amount of basic solution should be used to neutralize unreacted chlorine gas, so that this process is undesirable in terms of economical and environmental aspects. Moreover, when PIBSA having an increased chlorine content is used as a fuel additive, there are problems such as corrosion of internal combustion engine including an engine of automobile and discharge of chlorine through exhaust, so that an improvement is made by preparing a lubricating oil additive and fuel clarificant by using highly reactive polybutene.
Highly reactive polybutene is advantageous when the vinylidene content is high. The reason will be described with reference to typically known technique. At first, highly reactive polybutene is subjected to Ene reaction (or Alder-Ene reaction) with maleic anhydride at about 230° C. PIBSA produced by the reaction is reacted to alkyl amine to produce polyisobutenyl succinic imide (PIBSI). Then, the PIBSI is mixed with a diluent having a high boiling point to prepare a fuel clarificant and a lubricating oil additive. Since the vinylidene content of the highly reactive polybutene increases the PIBSA yield, as the vinylidene content increases, the quality increases. Consequently, the PIBSA yield is increased. Herein, high PIBSA yield means that the PIBSI yield is also high, which indicates that an active ingredient which acts as a clarificant is high. Therefore, it can be found that preparation of highly reactive polybutene having a high vinylidene content is important.
Evolution from non-reactive polybutene to highly reactive polybutene, which is used in a lubricating oil additive or fuel clarificant, improves the process by eliminating a step of reaction and is environmental friendly by excluding toxic chlorine gas (Cl2 gas). Therefore, to increase reactivity of polybutene per se, a study has been conducted to prepare highly reactive polybutene including 70% or more, and more preferably 85% or more vinylidene without chlorine which causes corrosion of a device. As a Friedel-Crafts type catalyst for preparing the highly reactive polybutene, boron trifluoride (BF3), which allows highly reactive polybutene having a relatively high vinylidene content than other lewis acids, is generally used. U.S. Pat. Nos. 4,605,808, 5,068,490, 5,191,044, 5,408,018, and 5,962,604 disclose a method for capable of preparing highly reactive polybutene having 70% or more, and preferably 80% or more of vinylidene by using boron trifluoride or a complex compound of boron trifluoride with a cocatalyst of water, ether, and alcohol.
In consideration of the documents described above, the molecular weight of the polymeric product has close relationship with the reactivity. In other word, when a complex catalyst having a low molar ratio of cocatalyst/main catalyst having high reactivity is used, a product having a high molecular weight may be produced. When a molar ratio of a complex catalyst is gradually increased, the activity of the catalyst is decreased, so that a product having a low molecular weight may be produced. In addition, it has been indirectly suggested that highly reactive polybutene including a high vinylidene content may be prepared by using a complex catalyst having declined reactivity due to a cocatalyst such as alcohol, and ether, thereby increasing reaction selectivity of isobutene.
U.S. Pat. No. 5,068,490 discloses a method for preparing polybutene having a vinylidene content of 80% or more by using, as a catalyst, a complex including boron trifluoride and ether having at least one tertiary alkyl group. The method has advantages in that isomerization is low even for long term contact. In the examples, it has been indicated that, when isopropyl t-butylether having both secondary and tertiary alkyl groups is used, the most excellent result is shown, but the isopropyl t-butylether is expensive and is not produced for conventional purpose so that self preparation is required. U.S. Pat. Nos. 5,408,018 and 5,962,604 disclose a method for preparing polybutene having 80% or more of vinylidene and low degree of molecular weight distribution by using, as a catalyst, a complex of secondary alcohol and boron trifluoride. However, there are many limitations in the operation condition such that contact is maintained for a short period of 9 minutes or less at a temperature equal to or less than −10° C. for operation rate control. Therefore, to increase the vinylidene content, there are many disadvantages in terms of an economical aspect in that an isobutene law material having high purity should be used and preparation should be performed by using a catalyst having a decreased activity.
U.S. Pat. No. 7,037,999 B2 discloses a polybutene having a vinylidene content of less than 70% and including a double bond at tetra position less than 10%, and a process for preparing the same. However, there is no mention about advantages obtained by the double bond at tetra position and a method for efficiently preparing polybutene in an economical aspect. In addition, in examples, considering that polybutene is prepared with a low conversion rate, high price of isobutene having high purity is used, however, polybutene is prepared at low yield in this case and thus the method is not economical. Additionally, C4 raffinate-1 containing 1-butene, and 2-butene is used, the conversion rate should be decreased a lot to prepare polybutene including less than 10% of tetra-substituted double bond content.
Tetra-substituted double bound, which is a branched alkyl structure, has excellent compatibility with fuel of internal combustion engine and lubricating oil and relatively good heat stability and reactivity than vinylidene or tri-substituted double bond during halogenation or epoxification for preparing a lubricating oil additive or fuel additive, so that the tetra-substituted double bound may be efficiently used to fields requiring high yield.
In the presence of various raw materials such as C4 raffinate-1, and high purity isobutene, polymerization and preparation of polybutene including a desired vinylidene content is almost impossible due to various limiting factors. Generally, non-reactive polybutene prepared by using, as a catalyst, aluminum trichloride (AlCl3) has a vinylidene content of 5 to 10%. Highly reactive polybutene prepared by using boron trifluoride (BF3, main catalyst), a cocatalyst of alcohol, and auxiliary cocatalyst of ether has 70% or more of vinylidene. As long as preparing non-reactive polybutene, it is very difficult to adjust the vinylidene content in a range of 70% or less. Therefore, it is required a method capable of easily adjusting the vinylidene content and molecular weight at a high conversion rate.